1. Field of the Invention
The present invention generally relates to improvements in centrifugal pellet dryers and more particularly to improvements in the rotor structure which includes the shaft, pellet lifter assemblies and supporting spiders which support the pellet lifter assemblies on the shaft.
2. Description of the Prior Art
Plastic pellets are typically formed in an underwater pelletizer in which molten polymer is extruded through orifices in a die plate and cut into pellets by a rotating knife assembly, all of which is located under water with the pellets and water being discharged from the under water pelletizer as a slurry. The slurry of pellets and water is then usually passed through a dewatering device to remove most of the water. However, the pellets are still wet and have some excess water associated therewith and are normally then dried by movement through a centrifugal pellet dryer.
Centrifugal pellet dryers are well known and have been in use for a number of years. Known centrifugal pellet dryer structures are disclosed in prior U.S. Pat. Nos. 3,458,045, 4,218,323, 4,565,015 and 5,265,347, which are owned by the assignee of this application. Attention is invited particularly to the latter two patents for a disclosure of prior dryers over which the present invention is an improvement. Such prior pellet dryers include a screen enclosure or drum of generally cylindrical configuration in which is mounted a rotor including a driven rotatable shaft with lifter assemblies associated with the screen and mounted on the shaft by spiders in a manner to elevate pellets from a lower inlet to an upper outlet. The centrifugal forces imparted to the pellets as they rise in the dryer cause water to be discharged through the screen for drainage to any desirable discharge point. Air is circulated through the pellets as they are lifted to facilitate the drying operation. The dried pellets are then discharged from a discharge at the upper end of a housing normally provided for the dryer.
While previously known centrifugal pellet dryers have functioned satisfactorily, the present invention increases the effective operation by providing novel pellet lifter assemblies and novel spiders which have greater strength, are lighter weight and designed to facilitate assembly and replacement of components. Thus, the present invention provides a less complicated and lighter and better balanced rotor structure for drying plastic pellets.